1. Field of the Invention
The present invention relates generally to thermal spraying internal combustion engines and, more specifically, to a method of staggering reversal of thermal spray inside a cylinder bore of an internal combustion engine.
2. Description of the Related Art
It is known to coat a surface of a cylinder bore for an internal combustion engine. Typically, thermal spray guns are conventionally supported and moved at a uniform speed to coat the surface. The thermal spray guns deposit a layer of sprayed material in a relatively thin coat to avoid concentrating undue heat in the surface. To build a greater thickness of the sprayed material, several passes of the thermal spray gun are necessary. If the thermal spray gun is immediately reversed in its uniform linear travel precisely at the end of the surface, a non-uniform bulge may occur in the coating at such reversal edge. Excess material is laid down at such reversal edge by the slowing down of the gun to make the reversal. This bulge is disadvantageous because (i) it introduces greater heat to the coating at such bulge, leading to possible "hot spots" or residual thermal stress, (ii) the bulging can possibly lead to disbanding as a result of an excessive shrinkage rate in the coating when the thermal spray gun moves away.
In an attempt to overcome this problem, the travel of the thermal spray gun is extended well beyond the surface for the coating (i.e., overspraying), before reversing the travel of the thermal spray gun. This results in considerable waste of spray material.
When spraying the internal combustion engine that cannot tolerate the presence of a coating outside the surface of the cylinder bore, one must, either (i) use expensive masking to prevent contaminating such other parts of the internal combustion engine that are not to be coated, (ii) use a release agent as well as tedious cleaning of the adjacent surfaces to remove the unwanted coating (cleaning is essential to remove the risk of loose particles adjacent and outside the edge of the cylinder bore, which particles may break loose and contaminate other moving parts of the internal combustion engine). Therefore, there is a need in the art to contain and reduce overspray when spraying a cylinder bore of an internal combustion engine.